1. Field of Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a system and method for stacking perforating guns to form a perforating string.
2. Description of Prior Art
Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In FIG. 1 a prior art perforating system 11 is shown having a perforating gun string 4 with perforating guns 6. The gun string 4 is shown disposed within a wellbore 1 on a wireline 5. The perforating guns 6 in the gun string 4 are usually coupled together by connector subs 13. A service truck 7 on the surface 9 generally accompanies perforating systems 11 for handling the upper end of the wireline 5. The wireline 5 typically is used for raising and lowering the gun string 4, as well as a communication means and control signal path between the truck 7 and the perforating gun 6. The wireline 5 is generally threaded through pulleys 3 supported above the wellbore 1. As is known, derricks, slips and other similar systems may be used in lieu of a surface truck for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems are also disposed into a wellbore via tubing, drill pipe, slick line, and/or coiled tubing.
Included with the perforating gun 6 are shaped charges 8 that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge 8 at very high velocity in a pattern called a “jet” 12. The jet 12 perforates the casing and the cement and creates a perforation 10 that extends into the surrounding formation 2.
Typically the gun string 4 is inserted within a lubricator that is then mounted on a wellhead assembly for deployment into a wellbore. The lubricator provides a pressure seal around the string 4 so the gun string 4 can be pressure equalized with the usually higher pressure wellbore prior to being deployed therein. In some instances space constraints at the well site may limit the height of the lubricator thereby in turn limiting the length of the gun string 4.